The groundbreaking agreement for Mr Kim and Mr Trump to meet came about as North Korea said it was committed to denuclearising the Korean peninsula.

Exactly what that would entail has remained unclear, but North Korea has invited foreign media to witness the dismantling of its main nuclear test site later this month.

What Kim wants

Mr Bolton recently said North Korea could follow a “Libya model” of verifiable denuclearisation, but this alarms Pyongyang, which watched Libya’s Colonel Gaddafi give up his nuclear programme only for him to be killed by Western-backed rebels a few years later.

The BBC’s Laura Bicker in Seoul says North Korea – which had long said its nuclear arsenal is essential for its survival as a state – is now making its demands clear.

The whole reason the North Korean state has spent years building up a nuclear arsenal, at such a great cost, is for survival.

So to compare denuclearisation in North Korea with Libya or indeed Iraq as John Bolton did on Sunday is not going to offer much comfort. Both regimes collapsed.

This is also a warning shot to the Trump administration. They will be aware how much Mr Trump wants this summit and how it is being spun as a success brought about by his maximum pressure strategy.

There were signs this boasting irritated Pyongyang, but now it has decided to speak out through someone in a position of power.

North Korea wants the world to know that it is coming to the negotiating table from a position of strength, and they may feel that they are making all the concessions.